The present invention relates to kiln fuel systems and, more particularly, kiln fuel systems which utilize combustible gas or fume generated by pyrolysis of waste material as a fuel source.
Pyrolysis is a well-known mechanism for treating toxic and otherwise hazardous waste having organic components. The waste material is heated in the absence of oxygen, or in an oxygen reduced atmosphere, to generate a combustible gas or fume. Since the pyrolysis of hazardous waste material generates combustible fume, it is appropriate to utilize a pyrolytic process to generate a combustible fume to be used as a fuel source for other processes.
Accordingly, it would appear appropriate to combine a pyrolytic process with a clinker kiln or cement process, since the latter requires the input of large amounts of heat energy. For example, the Ogawa et al. U.S. Pat. Nos. 4,295,823 and 4,627,877 disclose a rotary kiln which generates hot exhaust gas to power a heat-decomposer, and the combustible gas generated in the heat decomposer is burned in a preheater or calcinator. However, there is no mechanism disclosed for regulating the amount of heat energy input to the calcinator by fume from the heat decomposer, except for regulating the rate and amount of material entering the heat decomposer.
However, in order to generate high-quality cement material in such processes, it is necessary to maintain a temperature in the kiln within a relatively narrow range. A disadvantage of using pyrolytic fume generated from waste material is that the heating value of the fume produced may vary considerably. Consequently, when such fume is piped to a kiln--or generated therein--and ignited to provide an auxiliary heat source, the rate of heat energy input to the kiln varies accordingly.
Since a cement kiln requires that the temperature of the process be maintained within a relatively narrow range, it is necessary to adjust the heat energy input of the main fuel supply to the kiln in response to the variations and heating value of the pyrolytic fume. However, the contents of the kiln during the process comprise a large mass which retains large amount of heat energy, and it is not possible to monitor the temperature of the kiln directly and make such adjustments since the amount of heat energy retained resists rapid temperature changes. Consequently, systems exist in which a pyrolytic fume is used as an auxiliary fuel source, but in order to maintain the heating value of the fume within a predetermined range, extensive pretreatment of the pyrolytic material is required. For example, one such system requires separation, precrushing, and sorting of material prior to the pyrolytic process.
Accordingly, there is a need for a kiln system which can take advantage of the economic benefits of pyrolysis of hazardous industrial waste material by using the combustible fume so generated as an auxiliary fuel source, but can maintain the heating value of the fume substantially constant in order to maintain the temperature within the kiln within a predetermined operating range, without extensive pretreatment of the pyrolytic material, which tends to reduce the cost-effectiveness of the process.